This invention relates generally to apparatus for handling, sorting and testing electronic components and more particularly to a system for reliably making and breaking electrical connection, at a high repetition rate, between leads of a semiconductor device and contact pins in electrical connection with a load board.
In the manufacture of electronic components, particularly semiconductor devices such as digital integrated circuits (IC's), it is highly desirable to test each device before it is shipped and/or incorporated in a larger product. Production economics require that this handling and testing be accomplished at extremely high rates. Typical operating rates are in excess of 5,000 devices per hour. When operating at these speeds, testing of the device must be accomplished within an extremely short period of time, typically 100 milliseconds. Further, it is extremely important to have an accurate, precise, and reliable test. An increase in the uncertainty of the test also increases the likelihood of misclassifying a device that is, classifying as good a device that is in fact defective, or classifying as defective a device that is in fact good.
In the testing of three classes of semiconductor devices, digital fast switch devices such as bipolar circuits, digital clock rate devices such as high speed counters, and linear devices which operate at radio frequencies such as detectors for FM tuners, the physical separation between the device being tested and the test circuit of "load board" can significantly limit the precision and reliability of the test.
In digital applications, increases in the length of the conductive elements that connect a lead on the device to a corresponding pin connected to the load board can degrade the shape of the test signal and therefore the precision and accuracy of the test measurement. Increased contactor length also increases the time for a pulse to travel through the contact and therefore lowers the permissible repetition rate of the interrogating test pulses. A limitation on the pulse repetition rate can be a serious problem whenever a test procedure requires a large number of test pulses, as in the testing of memory devices where each of perhaps millions of addresses must be interrogated. At high frequencies long contacts can also enhance the problem of reflected signals since the time required to wait for the reflection to dissipate can severely limit the speed of the test.
In the testing of linear devices such as detectors for FM tuners, the test must be performed "in-situ," that is, in the actual end use environment. Ideally a device to be tested is manually connected in the actual circuit. Since this is very time consuming, it has been found acceptable to test the device close to the actual end use circuit. Generally the separation between actual circuit, simulated by a load board or test fixture, and the point of connection to the leads on the device must be no more than approximately one inch or 25.4 millimeters. Where the test fixture has relatively large physical dimensions, the difficulties in achieving this degree of closeness are complicated by the further requirement that the electrical connection must be made while presenting to the test fixture an essentially unrestricted mating surface or "load plane."
While prior art devices having relatively short test contacts and an unrestricted load plane are known in the art, they suffer from various disadvantages. These connection systems are characterized by flexible contacts that have one end fixed, typically the end in direct electrical connection with the load board, while the free ends are flexed into or out of contact with the leads on the device. One such system utilizes a pair of opposed contact arms that are urged against an interposed lead by a spring force inherent in the contact arm. Connection is broken by a rotating cam element also located between each contact arm pair. This system suffers from a relatively low contact force on the leads, metal fatigue of the arms at the bend point near fixed ends, poor contact location on the leads (on the tip or free end rather than on the shoulder adjacent the device), and a reduced ability to cope with normally occurring variations in the location of the leads.
Another system pushes the contacts, usually in spaced pairs, laterally into connection with the leads against an inherent spring force of the contacts that urges them away from the leads. While this system lends itself to a shoulder connection on the leads, it also suffers from a bending fatigue in the contact arms. This system also does not achieve a consistently good, high force contact at both connections over a range of lead positions normally encountered. Another related problem with both of these "fixed-end" systems is that arrangements that tend to reduce the bending and/or enhance the contact force are more likely to cause severly misaligned leads to catch on the contacts and interrupt the entire testing and handling process.
It is therefore a principal object of this invention to provide a test contactor system for a high speed semiconductor handler that has relatively short contacts and provides an unlimited load plane, while minimizing the problem of metal fatigue, providing a high contact force over a wide range of lead positions, and establishing contact with the lead at the shoulder location.
Further objects of the invention are to provide a test contact system with the aforesaid advantages that operates in a precisely controlled fashion, allows the contacts to be conveniently changed or repositioned with respect to the load board, and has a long operational life.